Maybe it's just my computer, because I tried summoning a horse with the /summon EntityHorse command, and i was still unable to ride it, even in 1.8pre-3, so i'm a bit out of it, not something i'm too worried about though. I don't ride horses often
<==EDIT==>
I tried again, and succeeded. I guess this is MC-61535 Sorry for the trouble.
Maybe it's just my computer, because I tried summoning a horse with the /summon EntityHorse command, and i was still unable to ride it, even in 1.8pre-3, so i'm a bit out of it, not something i'm too worried about though. I don't ride horses often
<==EDIT==>
I tried again, and succeeded. I guess this is MC-61535
Sorry for the trouble.